Luhn algorithm | C # program to implement Luhn algorithm ; Returns true if given card number is valid ; We add two digits to handle cases that make two digits after doubling ; Driver code
using System ; class GFG { static bool checkLuhn ( String cardNo ) { int nDigits = cardNo . Length ; int nSum = 0 ; bool isSecond = false ; for ( int i = nDigits - 1 ; i >= 0 ; i -- ) { int d = cardNo [ i ] - '0' ; if ( isSecond == true ) d = d * 2 ; nSum += d / 10 ; nSum += d % 10 ; isSecond = ! isSecond ; } return ( nSum % 10 == 0 ) ; } static public void Main ( ) { String cardNo = "79927398713" ; if ( checkLuhn ( cardNo ) ) Console . WriteLine ( " This ▁ is ▁ a ▁ valid ▁ card " ) ; else Console . WriteLine ( " This ▁ is ▁ not ▁ a ▁ valid ▁ card " ) ; } }